Conventionally, a seat apparatus is known which includes a height adjusting mechanism. An occupant who sits on a seat provided with the aforementioned seat apparatus can set a seat height in response to one's physical size. Further, the seat apparatus is provided with a lock mechanism for controlling a seat operation for preventing upward and downward movement of the seat in case of a vehicle crash.
One of the known seat apparatus of this type is described in FR2796602A which includes a so-called vertical lock mechanism having a tension member, a cam, a lock member, and a link provided with a gear on its side portion. The tension member is connected to a seat belt anchor serving as a seat belt base, the cam is pivotally supported so as to be movable in response to the tension member, the lock member can change a condition of unlock and lock by activation of the cam, and the link is engagable with the lock member and connects a seat to a floor.
However, the seat apparatus described in FR2796602A is necessary to go through the following process for operating the lock mechanism. First, a tensile force of the seat belt anchor is transmitted to the tension member, then the tension member rotates the cam, and then an engaging member engages with a gear provided on side portion of the link by rotation of the cam. Because a lock condition is achieved through operations of large numbers of members, a play of a part at which each member is engaged tends to become larger, and the seat operation in an emergency may be delayed to be locked or uncertainly be locked. Moreover, when the seat apparatus includes large numbers of operating members, an incidence of failure is increased and manufacturing cost of the seat apparatus being expensive.
A need thus exists for a seat apparatus which is configured to improve reliability of the seat operation lock in an emergency, to reduce the incidence of failure, and to manufacture the seat apparatus at a low cost.